Agreed, though you don't even need to go that far. You can just point to X2. Jean Grey dies in that film, and no one threw a fit. In fact, plenty of Hypsters have listed it as one of their favorite scenes of the trilogy, so why the aversion to similar deaths in Days of Future Past? This isn't The Last Stand, where characters who shouldn't die are given cheap deaths just to "round out" their characters and close out the trilogy. The deaths of Days of Future Past are part of the story and do serve a purpose--or at least a better one, in my opinion. Plus, like Jean Grey in X2, we know there is most likely a possibility of them coming back.